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In article <1990Aug22.171934.24558@zoo.toronto.edu>, henry@zoo.toronto.edu (Henry Spencer) writes:
> >Are switches supposed to spark when you switch them? ...
> 
> It's pretty much inevitable when they are carrying noticeable currents.
> (Breaking the arc is the dominant design problem of really big circuit
> breakers, in fact -- when you try to cut off a circuit carrying, say,
> 1000 A at 50 kV, you get some impressive sparks! :-))

	Outdoor high voltage switches usually contain a "horn gap" which
spreads as the switch is opened, thereby specifically directing the arc
away from the actual current-carrying switch contacts.

	Other types of high voltage switches (non-oil filled type), such
as those contained in metal clad switchgear, sometimes use a source of
compressed air to blow out the arc at the time the switch is opened.
The compressed air valve is triggered by the switch controller.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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